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MC_MotionInPosition position offset

9/4/2023 9:44 AM	Rate (0)
roald87 Posts: 4 Rating: (0)	I'm trying to move a linear axis using MC_MotionInPosition. I calculate a trajectory with new setpoints for the position, speed and acceleration every 16 ms. When I then execute a trajectory, is never reaches the exact position and the offset becomes worse when I move at higher speeds. For example, I want to move 10 cm back and forth. After the motion profile isexecuted, the actual position is a few mm away from the final set position. I guess this happens, because the velocity is set to zero at the end of the trajectory. If the position was not reached at that point, the controller can't correct for it anymore. A solution I thought of was to use MC_MoveSuperimposed to correct for any offsets. This works if I activate the MC_MoveSuperimposed block if no MC_MotionInPosition trajectory is executed. If I use them simultaneously, the MC_MoveSuperimposed output CommandAborted is set to true after a few cycles. When I read the documentation and it should be possible to use both these functions in parallel. Am I doing something wrong?
roald87 Posts: 4 Rating: (0)
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9/4/2023 11:12 AM	Rate (0)
jacek d Platinum Member Joined: 9/23/2005 Last visit: 9/15/2025 Posts: 5116 Rating: (768)	It looks to me like not optimized controllers. And maybe the axis not in the DSP mode. Have look at this.
	Regards, Jacek What is confusing you is the fact that you never see a number but always its digit representation. So you end up thinking that the number is the representation. - Andrej Bauer Any claims against me - based on whatever legal reason - resulting from the use of any code and/or ideas presented on this forum shall be excluded. #StayWithUkraine
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9/4/2023 12:47 PM	Rate (0)
roald87 Posts: 4 Rating: (0)	Hi Jacek Thanks for the ideas. We tuned the controller, but that didn't have any noticeable effect. Let me double check that it is in DSP mode. Roald
roald87 Posts: 4 Rating: (0)
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9/4/2023 2:03 PM	Rate (0)
jacek d Platinum Member Joined: 9/23/2005 Last visit: 9/15/2025 Posts: 5116 Rating: (768)	Another idea. How does the axis behave when operated from its commissioning panel in the Scout ? Do you experience such substantial following error too ?
	Regards, Jacek What is confusing you is the fact that you never see a number but always its digit representation. So you end up thinking that the number is the representation. - Andrej Bauer Any claims against me - based on whatever legal reason - resulting from the use of any code and/or ideas presented on this forum shall be excluded. #StayWithUkraine
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9/4/2023 3:13 PM	Rate (0)
roald87 Posts: 4 Rating: (0)	DSP mode is enabled. Not sure how it behaves in the scout, but when I move the axis using the MC_MoveAbsolute the axis goes to the exact position.
roald87 Posts: 4 Rating: (0)
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